A study carried out in the French West Indies, where the drink is popular, found many patients with "atypical parkinsonism" as a result.

The conditions found were often as deadly as the progressive brain disorder, but started at an earlier age, and were resistant to standard Parkinson's Disease treatments.

Some patients' conditions improved when they stopped drinking the tea.

Natural insecticide

It is suggested that the tea, made from the Annonaaceae family of fruits, examples of which are the custard apple and pawpaw, is toxic to the human nervous system.

Experiments in laboratories on animals have found that the active ingredient, a natural insecticide, causes nerve damage.

In the French West Indies, they are thought to have purgative or even aphrodisiac qualities and are mainly drunk by older men.

The tea is also used for its sedative and hypnotic medicinal qualities.

The study found that of 87 patients complaining of Parkinsonian symptoms such as tremor, rigidity and balance problems, 22 had conventional Parkinson's Disease.

The rest were suffering from "progressive supernuclear palsy" or other forms of atypical parkinsonism.

These illnesses showed little or no response to levadopa, the principal treatment for Parkinson's.

The researchers concluded that there was a "strong association" between the fruit teas and Parkinsonism.

And the fact that five of the patients had a family history of similar diseases suggested to them that some people were genetically susceptible to the toxin in the drink.